Enhances autosave controller with missing features:
- prime(payload): Sets initial hash baseline to prevent autosaves on page load
- idleResetMs option: Auto-transitions from 'saved' → 'idle' status (default 2s)
- onSaved callback: Now receives { prime } helper for re-priming after server response
- Cleanup: destroy() now properly clears idle reset timer
All existing tests pass. Backward compatible - forms not using new features yet.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>
